Semen microbiota are dramatically altered in men with abnormal sperm parametersOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study explored whether the semen microbiome differs with abnormal semen analysis parameters. The cause of abnormal semen findings is unidentified in about 30 percent of cases, and the semen microbiome may help explain the gap. The design was a cross-sectional observational study of men undergoing fertility evaluation or vasectomy consultation. Semen was analyzed by World Health Organization 5th Edition criteria. Bacteria were profiled by next-generation 16S ribosomal RNA sequencing of the V1-V2 regions. Differential abundance used ANCOM-BC, with canonical correlation analysis for continuous associations.
Who was studied?
The cohort was 73 men aged 18 or older recruited at a single University of California, Los Angeles center between August 2021 and June 2022. Some had proven biological paternity before vasectomy. Mean age was about 37.9 years and mean body mass index about 26.7. Seventy-eight percent were circumcised. Men were stratified by semen parameters rather than recruitment source. Groups compared normal versus abnormal sperm concentration and motility. There were no significant differences in age, body mass index, circumcision, smoking, or alcohol across comparison groups.
What were the most important findings?
Men with abnormal sperm motility had a higher abundance of Lactobacillus iners than men with normal motility (9.4 versus 2.6 percent, p = 0.046). This link persisted in canonical correlation analysis (r = 0.392, p = 0.011). Men with abnormal sperm concentration had more Pseudomonas stutzeri (2.1 versus 1.0 percent, p = 0.024) and Pseudomonas fluorescens (0.9 versus 0.7 percent, p = 0.010), but less Pseudomonas putida (0.5 versus 0.8 percent, p = 0.020). No significant differences in alpha or beta diversity appeared across groupings, pointing to subtle shifts in specific species rather than global dysbiosis.
What are the greatest implications of this study?
The results suggest a small set of species, most notably Lactobacillus iners, may relate to impaired sperm parameters. This is reported as the first negative association between Lactobacillus iners and male-factor fertility. Different Pseudomonas species tracked in opposite directions, indicating that members of one genus need not act alike. Because the design was cross-sectional and observational, causation cannot be inferred. Single-site recruitment, one sample per man, and no data on recent antibiotics or infections limit generalizability.